Field of the Invention
The present invention relates to a display device and a method of driving the same, and particularly, to a display device where a touch panel is integrated within a panel and a method of driving the same.
Discussion of the Related Art
Touch panels are coordinate input devices. Touch panels are attached to display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED), and electrophoretic displays (EPDs). A touch panel enables a user to input information by directly touching the touch panel with a finger, a pen or the like while looking at the screen of the display device.
A method of manufacturing an LCD device including a touch panel includes an add-on type, where a panel is configured to display an image and a touch panel that is configured to determine a touch event are separately manufactured and bonded to each other, and an in-cell type where the touch panel is built into the panel for displaying an image.
Recently, the demand for an in-cell type display device, in which a touch panel is integrated into a panel for slimming portable terminals such as smart phones and tablet personal computers (PCs), is increasing.
The in-cell type display device may be divided into a mutual-capacitance type and a self-capacitive type.
FIG. 1 is an exemplary diagram illustrating a related art self-capacitance display device.
The related art self-capacitance display device, illustrated in FIG. 1, includes a panel 10, where a touch panel 50 includes a plurality of self-capacitance electrodes 51, and a touch sensing unit 60 configured to determine a touch event by supplying a touch voltage to the touch panel 50. A plurality of touch lines 52 that connect the self-capacitance electrodes 51 to the touch sensing unit 60 are arranged in parallel with a plurality of data lines which are provided in the panel 10. For example, a vertical direction is a direction parallel to a data line, and a horizontal direction is a direction parallel to a gate line 21 as illustrated in FIG. 1. The term “touch event” may be referred as “whether there is a touch on the panel”.
A plurality of touch groups 53 comprising a plurality of self-capacitance electrodes 51 are arranged along the data lines. The touch groups 53 are driven by a multiplexers (MUX1 to MUX3) 61 of the touch sensing unit 60.
The touch groups 53 are extended along the vertical direction of the panel 10. The touch groups 53 are positioned in series along the horizontal direction of the panel 10. Therefore, a gate line is extended through all of the touch groups 53 of the panel 10.
In the related art self-capacitance display device, display-to-touch crosstalk (DTX) problemoccurs. The term DTX preferably means a level of touch raw data (e.g. magnitude of the sensed touch signal) is shifted due to a change of the charged capacitance of a liquid crystal. For example, the charged capacitance of the liquid crystal may be changed when an image data is refreshed by every frame. When a data voltage is supplied to a pixel electrode through a data line, the liquid crystal is affected by the data voltage applied to the pixel electrode and a common electrode (e.g. self-capacitance electrodes) is affected through the liquid crystal, in term of parasitic capacitance. That is, an electric field is generated between the pixel electrode and the common electrode to derive the liquid crystal for displaying an image may cause unwanted noise for the touch. Consequently, DTX is occurred within the panel 10 and the DTX may be affected to the touch panel 50 which is attached to the panel 10.
In addition, the magnitude of the DTX is seriously increased when the touch panel 50 is integrated into the panel 10. This is because the self-capacitance electrodes 51 are configured with the common electrode of the panel 10.
For example, when an image is refreshed from a black image (0th Gray level), which may be referred as the lowest gray level (e.g. 8-bit image format), to a white image (255th Gray level), which may be referred as the highest gray level (e.g. 8-bit image format), for one frame period, a gap between two different gray levels may represent the magnitude of the DTX. For example, the black to white change may be referred as the maximum magnitude of the DTX. In addition, the magnitude of the DTX may be proportional to the gap between the gray level of the previous frame (e.g. black image) and the gray level of the current frame (e.g. white image) of a pixel.
A method, which analyzes pattern information of an image when touch sensing is being performed and compensates for a level of a sensing signal on the basis of the analyzed pattern information, is used for compensating for DTX.
However, in the related art self-capacitance display device as illustrated in FIG. 1, when touch sensing is being performed with the touch groups 53 which are arranged along the data lines, a method of compensating for DTX becomes very complicated. For this reason, a memory size associated with DTX compensation needs to be increased, and a complexity of calculation is also increased. Consequently, there are many difficulties to eliminate the DTX and a large compensation error may occur.
In other words, in the related art self-capacitance display device as illustrated in FIG. 1, the arrangement of the touch groups 53 is mismatched with the arrangement of the pixels within the panel 10. Therefore, for every touch sensing period, the compensation data needs to be updated. For this reason, a large compensation error may occur.
Moreover, in the panel 10 where the touch groups 53 are arranged in a vertical direction, the touch lines 52 that connect the self-capacitance electrodes 51 to the touch sensing unit 60 are arranged in parallel with the data lines. Therefore, a parasitic capacitance C occurs between the touch lines 52 and the data lines, causing touch noise.
Moreover, the self-capacitance type touch panel is more sensitive than the mutual-capacitance type touch panel in terms of DTX noise. Therefore, the DTX noise should be eliminated for implementing the self-capacitance type.
Moreover, when the self-capacitance type touch panel is implemented as an in-cell type, the magnitude of the DTX noise may be significantly increased. Therefore, the DTX noise should be eliminated for implementing the in-cell type self-capacitance touch panel.